Chemistry Reference
In-Depth Information
Figure 1.
Separation diagram by crystallizability. a) TREF separation process, b) Dynamic crystallization, c) Crystallization
elution fractionation.
sample was loaded, and 3) Elution cycle
where a solvent flow,
segregated and anchored on the support
while the other components, still in solu-
tion, move along the column until they
reach their own crystallization tempera-
ture. At the end of the crystallization cycle,
the three components are separated inside
the column according to crystallizability.
The flow rate in during crystallization,
F
c
, plays an important role as it has to be
adapted to the crystallization rate,
F
e
, is passed through
the column to elute the fractions being
dissolved as the temperature rises. The
three components of the blend are physi-
cally separated from each other in the last
cycle as shown in Figure 1.a.
A new separation approach is presented
here based on the same principles of
crystallizability and using a packed column
like in TREF, but performing the physical
segregation of fractions in the crystalliza-
tion step as in CRYSTAF. The new
separation process is known as dynamic
crystallization because the cooling is per-
formed while a small flow of solvent is
passed through the column.
Dynamic crystallization is also a three-
step procedure as represented in Figure 1.b,
but physical separation of the components
takes place within the column itself in the
crystallization cycle. In dynamic crystal-
lization, a small solvent flow, F
c
, is passed
through the column during crystallization,
in such a way that when a component
reaches its crystallization temperature it is
C
r
,
crystallization temperature range,
D
T
c
,of
the components to be separated, and
column volume,
V
c
, in order to crystallize
all the components within the column
length; F
c
is calculated as follows from
Equation (2):
V
c
D
T
c
C
r
F
c
ΒΌ
(2)
Once the crystallization cycle is com-
pleted, the flow is interrupted and the
column is heated for a few minutes at a
temperature where all components are
dissolved. After that, the elution cycle
begins by adding a proper elution flow to
the column. The separation order of
